Bone fixation system and method for using the same

ABSTRACT

A tulip assembly configured to be coupled to a head of a bone fixation device includes at least one inner member configured to fix the tulip assembly to the head of a bone fixation device, and an outer member including at least one engagement surface configured to selectively fix a rod in the tulip assembly via rotation of the outer member.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/258,831 titled “Pedicle Screw Systems and Methods ofAssembling/Installing the Same” filed on Oct. 25, 2005, which isincorporated herein by reference in its entirety.

FIELD

The present system and method relate to bone fixation devices. Moreparticularly, the present system and method provide for a screw assemblyconfigured to facilitate the internal fixation of vertebral bodies.

BACKGROUND

Various devices for internal fixation of bone segments in the human oranimal body are known in the art. One type of system is a pedicle screwsystem, which is sometimes used as an adjunct to spinal fusion surgery,and which provides a means of gripping a spinal segment. A conventionalpedicle screw system comprises a pedicle screw and a rod-receivingdevice. The pedicle screw includes an externally threaded stem and ahead portion. The rod-receiving device couples to the head portion ofthe pedicle screw and receives a rod (commonly referred to as adistraction rod). Two such systems are inserted into respectivevertebrae and adjusted to distract and/or stabilize a spinal column, forinstance during an operation to correct a herniated disk. The pediclescrew does not, by itself, fixate the spinal segment, but insteadoperates as an anchor point to receive the rod-receiving device, whichin turn receives the rod. One goal of such a system is to substantiallyreduce and/or prevent relative motion between the spinal segments thatare being fused.

Although conventional prior art pedicle screw systems exist, they lackfeatures that enhance and/or benefit newer, minimally invasive surgery(MIS) techniques that are more commonly being used for spinal surgeries.It has been suggested that one possible advantage of an MIS approach isthat it can decrease a patient's recovery time.

Conventional pedicle screw systems and even more recently designedpedicle screw systems have several drawbacks. Some of these pediclescrew systems are rather large and bulky, which may result in moretissue damage in and around the surgical site when the pedicle screwsystem is installed during surgery. The prior art pedicle screw systemshave a rod-receiving device that is pre-operatively coupled or attachedto the pedicle screw. In addition, some of the prior art pedicle screwsystems include numerous components that must all be carefully assembledtogether. Further, traditional pedicle screw systems are pre-operativelyassembled, which makes these systems more difficult to install andmaneuver in a spinal operation where MIS techniques are used.

SUMMARY

An exemplary tulip assembly configured to be coupled to a head of a bonefixation device includes at least one inner member configured to fix thetulip assembly to the head of a bone fixation device, and an outermember including at least one engagement surface configured toselectively fix a rod in the tulip assembly via rotation of the outermember.

According to another exemplary embodiment, a tulip assembly configuredto be coupled to a head of a bone fixation device includes at least oneinner member configured to fix an angular position of the tulip assemblyrelative to the bone fixation device and an outer member including atleast one engagement surface configured to selectively fix a rod in thetulip assembly via rotation of the outer member. According to thisexemplary embodiment, the fixation of an angular position of the tulipassembly relative to the bone fixation device and the rod fixation aretemporally separate operations.

According to yet another exemplary embodiment, a tulip assemblyconfigured to be coupled to a head of a bone fixation device includes:an outer housing member including an upper portion and a lower portionhaving an internal tapered edge in the lower portion, a first innermember disposed in a lower portion of the outer member, the first innermember being elastically expandable to receive the head of a bonefixation device, a second inner member disposed in an upper portion ofthe outer member, the second inner member being configured to receive adistraction rod, wherein the first inner member includes an externaltapered edge and an internal tapered edge, the external tapered edgebeing configured to mate with the internal tapered edge of the outerhousing member to compress the first inner member.

A pedicle screw system, according to one exemplary embodiment disclosedherein, includes a pedicle screw having a threaded portion and a headportion, and a tulip assembly including at least one inner memberconfigured to fix said tulip assembly to the head portion, and an outermember including at least one engagement surface configured toselectively fix a rod in the tulip assembly via rotation of the outermember.

Similarly, a method of fixing a tulip assembly to a pedicle screwincludes inserting the pedicle screw into a bone, the pedicle screwincluding a head portion, expanding a first inner member over and headportion of the pedicle screw after the pedicle screw is inserted into abone, fixing an angle of the tulip assembly relative to the pediclescrew using the first inner member and a second inner member, insertinga rod into the tulip assembly, and positionally locking the rod in thetulip assembly after the angle is fixed by rotating an outer member ofthe tulip assembly including at least one rod engagement surface.

Another exemplary method of fixing a tulip assembly to a pedicle screwincludes inserting the pedicle screw into a bone, the pedicle screwincluding a head portion, expanding a first inner member over and headportion of the pedicle screw after the pedicle screw is inserted into abone, fixing an angle of the tulip assembly relative to the pediclescrew using the first inner member and a second inner member, andpositionally locking a rod in the tulip member after the angle is fixed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various exemplary embodiments ofthe present system and method and are a part of the specification.Together with the following description, the drawings demonstrate andexplain the principles of the present system and method. The illustratedembodiments are examples of the present system and method and do notlimit the scope thereof.

FIG. 1 is an assembled perspective view of a pedicle screw system,according to one exemplary embodiment.

FIG. 2 is an exploded perspective view of a pedicle screw system,according to one exemplary embodiment.

FIG. 3 is a perspective view of a pedicle screw, according to oneexemplary embodiment.

FIG. 4 is a perspective view of a tulip assembly of the pedicle screwsystem of FIG. 1, according to one exemplary embodiment.

FIG. 5 is an exploded perspective view of the tulip assembly of FIG. 4,according to one exemplary embodiment.

FIG. 6 is an exploded cross-sectional side view of the pedicle screwsystem of FIG. 4, according to one exemplary embodiment.

FIGS. 7A and 7B are a perspective view and a cross-sectional side-viewrespectively of a tulip body, according to one exemplary embodiment.

FIGS. 8A and 8B are a perspective view and a cross-sectional side-viewrespectively of an inner tulip member, according to one exemplaryembodiment.

FIGS. 9A and 9B are a perspective view and a cross-sectional side-viewrespectively of an expansion/contraction member or split ring, accordingto one exemplary embodiment.

FIG. 10 is a flow chart illustrating a method for securing a tulipassembly on a pedicle screw, according to one exemplary embodiment.

FIG. 11 is a cross-sectional side view of the components of a pediclescrew system prior to assembly, according to one exemplary embodiment.

FIGS. 12A and 12B are a perspective view and a cross-sectional side-viewrespectively of the pedicle screw system of FIG. 10 with the tulipassembly coupled to a head of a pedicle screw, according to oneexemplary embodiment.

FIGS. 13A and 13B are a perspective view and a cross-sectional side-viewrespectively of the pedicle screw system of FIG. 10 as the tulipassembly is retained during reduction of the expansion/contractionmember, according to one exemplary embodiment.

FIGS. 14A and 14B are a perspective view and a cross-sectional side-viewrespectively of the provisional locking of the tulip assembly, accordingto one exemplary embodiment.

FIGS. 15A and 15B are a perspective view and a cross-sectional side-viewrespectively of the rotation of the tulip body to retain a rod,according to one exemplary embodiment.

FIGS. 16A and 16B are a perspective view and a cross-sectional side-viewrespectively of the rotation of the tulip body to finally lock the rod,according to one exemplary embodiment.

Throughout the drawings, identical reference numbers designate similarbut not necessarily identical elements.

DETAILED DESCRIPTION

The present specification describes a system and a method for separatelylocking the orientation of a tulip assembly relative to a pedicle screwand locking a positional location of a rod in the tulip assembly.Further, according to one exemplary embodiment, the presentspecification describes the structure of a tulip assembly configured tobe placed on the head of a pedicle screw after placement of the pediclescrew in a patient's body and configured to receive and positionallysecure a top loaded rod. Further details of the present exemplary systemand method will be provided below.

By way of example, pedicle screw systems may be fixed in the spine in aposterior lumbar fusion process via minimally invasive surgery (MIS)techniques. The systems are inserted into the pedicles of the spine andthen interconnected with rods to manipulate (e.g., correct thecurvature, compress or expand, and/or structurally reinforce) at leastportions of the spine. Using the MIS approach to spinal fixation and/orcorrection surgery has been shown to decrease a patient's recovery timeand reduce the risks of follow-up surgeries.

The ability to efficiently perform spinal fixation and/or correctionsurgeries using MIS techniques is enhanced by the use of pedicle screwsystems provided in accordance with the present exemplary systems andmethods, which systems and methods provide a number of advantages overconventional systems. For example, a pedicle screw system in accordancewith one embodiment of the present exemplary system and method providesthe advantage that the pedicle screw may be inserted into the bonewithout being pre-operatively coupled with the rod-coupling assembly(hereinafter referred to as a tulip assembly). This is advantageousbecause the surgeon often needs to do other inter-body work afterinserting the pedicle screw, but before attaching the larger and bulkiertulip assembly. Such an advantageous pedicle screw system may be evenmore crucial when using MIS techniques because the inter-body spatialboundaries in which the surgeon must work may be quite limited.

In addition, pedicle screw systems in accordance with severalembodiments of the present system and method advantageously allow a userto initially fix (e.g., lock) the tulip assembly to the pedicle screw ata desired angle before inserting and/or capturing the rod. Initiallylocking the tulip assembly to the pedicle screw means that at least oneof the components of the tulip assembly is manipulated to grip and/orclamp onto the pedicle screw to reduce and/or prevent any translationaland/or rotational movement of the tulip assembly relative to the pediclescrew. The ability to initially lock the tulip assembly to the pediclescrew may facilitate the surgeon in performing compression and/ordistraction of various spinal and/or bone sections.

The term “distraction,” when used herein and when used in a medicalsense, generally relates to joint surfaces and suggests that the jointsurfaces move perpendicular to one another. However when “traction”and/or “distraction” is performed, for example on spinal sections, thespinal sections may move relative to one another through a combinationof distraction and gliding, and/or other degrees of freedom.

Another advantageous feature of at least one embodiment of the presentexemplary system and method is that an all-inclusive tulip assembly thatcan be coupled to the head portion of the pedicle screwintra-operatively is disclosed. This advantageous tulip assembly mayinclude the aspects or features that enable the tulip assembly to beinitially locked onto the head portion of the pedicle screw and then tofurther receive, capture, and finally lock the rod into the tulipassembly. In one exemplary embodiment, the tulip assembly is initiallylocked onto the head portion of the pedicle screw after the rod has beenreceived in the tulip assembly. This advantageous tulip assembly maydecrease the complexity of the pedicle screw system installation byreducing the installation to essentially a three-step process including,inserting the pedicle screw into bone, initially locking the tulipassembly onto the pedicle screw, which may be accomplished with orwithout the rod in the tulip assembly, and then capturing and lockingthe rod into the tulip assembly. In addition to accommodating the newMIS approach to spinal correction and/or fusion, the present exemplarysystem and method are configured to eliminate instances ofcross-threading and/or post-operative tulip splaying, which occurs whenthe amount of stress/strain in rod, which may be caused bypost-operative back flexion forces open the tulip assembly andeventually leads to the disassembly and/or the failure of the pediclescrew system.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present system and method for separately lockingthe orientation of a tulip assembly relative to a pedicle screw and apositional location of a rod in the tulip assembly. It will be apparent,however, to one skilled in the art that the present method may bepracticed without these specific details. Reference in the specificationto “one embodiment” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. The appearance of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment.

Exemplary Overall Structure

While the present system and method may be practiced by or incorporatedinto any number of bone fixation systems, the present system and methodwill be described herein, for ease of explanation only, in the contextof a pedicle screw system. Accordingly, the present system and methodincludes, according to one exemplary embodiment illustrated in FIG. 1, apedicle screw system (100) including a pedicle screw (102), a rod (104),and a coupling assembly (106), herein after referred to as a tulipassembly (106). According to one exemplary embodiment of the presentsystem and method, the tulip assembly (106) is configured to separatelylock the orientation of the tulip assembly (106) relative to the pediclescrew (102) and the positional location of the rod (104) in the tulipassembly (106). Operation of the tulip assembly (106) as well as itsinteraction with both the pedicle screw (102) and the rod (104) will bedescribed in further detail below with reference to the Figures.

According to one exemplary embodiment, FIG. 1 generally shows a pediclescrew system (100) comprising a pedicle screw (102), a rod (104), and acoupling assembly (106), hereinafter referred to as a tulip assembly(106). As illustrated in FIG. 1, the pedicle screw system (100) isconfigured to securely couple the tulip assembly (106) to the pediclescrew (102), thereby locking or fixing the tulip assembly (106) in arelative angular position (107) relative to the pedicle screw (102).Additionally, as shown in FIG. 1, the present exemplary pedicle screwsystem (100) is configured to receive a rod (104) and positionally fixthe rod (104) in the tulip assembly (106).

FIG. 2 illustrates an exploded view of the present pedicle screw system(100), according to one exemplary embodiment. As illustrated in FIG. 2,the coupling assembly or tulip assembly (106) of the pedicle screwsystem (100) includes a number of components configured to perform theabove-mentioned angular and positional fixing including, but in no waylimited to, a tulip body (132), an inner member (134), and anexpansion/contraction member (136) configured to engage the head portion(110) of the pedicle screw (102), as described in further detail below.Detailed descriptions of each component of the present pedicle screwsystem (100) will be described in further detail below, with referenceto FIGS. 3 through 9B.

FIG. 3 further illustrates the components of a pedicle screw (102),according to one exemplary embodiment. As illustrated in FIG. 3, thepedicle screw (102) includes an elongated, threaded portion (108) and ahead portion (110). Although pedicle screws (102) are generally known inthe art, the head portions (110) may be of varying configurationsdepending on what type of tulip assembly (160) is to be coupled to thepedicle screw (102). The head portion (110) of the present exemplarypedicle screw (102) includes a driving feature (124) and a maximumdiameter portion (126). The driving feature (124) of the presentexemplary pedicle screw (102) permits the screw to be inserted into apedicle bone and/or other bone. According to one exemplary embodiment,the pedicle bone is a part of a vertebra that connects the lamina with avertebral body. Additionally, according to the present exemplaryembodiment, the driving feature (124) can be used to adjust the pediclescrew (102) prior to or after the tulip assembly (106) is coupled to thepedicle screw (102). In the illustrated embodiment, the head portion(110) of the pedicle screw (102) is coupled to the threaded portion(108) and includes a generally spherical surface (127) with a truncatedor flat top surface (128).

In one exemplary embodiment, the pedicle screw (102) is cannulated,which means a channel (130) (shown in dashed lines and extending axiallythrough the pedicle screw (102)) extends through the entire length ofthe pedicle screw (102). The channel (130) allows the pedicle screw(102) to be maneuvered over and receive a Kirschner wire, commonlyreferred to as a K-wire. The K-wire is typically pre-positioned usingimaging techniques, for example, fluoroscopy imaging, and then used toprovide precise placement of the pedicle screw (102). While the pediclescrew (102) illustrated in FIG. 3 includes a number of components,numerous variations may be made including, but in no way limited to,varying the type of driving feature (124), varying materials, varyingdimensions, and the like.

Returning again to FIG. 1, the pedicle screw system includes a tulipassembly (106) configured to separately lock the orientation of thetulip assembly (106) relative to the pedicle screw (102) and thepositional location of the rod (104) within the tulip assembly (106).FIGS. 4, 5, and 6 illustrate the various components of the presentexemplary tulip assembly (106), according to one exemplary embodiment.FIG. 4 illustrates an assembled view of the tulip assembly (106). Asillustrated in FIG. 4, the present exemplary tulip assembly (106)includes a tulip body (132) substantially housing an inner member (134)and an expansion/contraction member (not shown). Additionally, a bore(138) is defined in the center of the tulip assembly (106) to provideaccess to the driving feature (124; FIG. 3) of a pedicle screw (102;FIG. 3) and/or a K-wire. FIGS. 5 and 6 further illustrate an explodedassembly view and an exploded cross-sectional assembly view of the tulipassembly (106) respectively. As illustrated in FIGS. 5 and 6, the tulipbody (132), the inner member (134), and the expansion/contraction member(136) each have a number of elements that work to provide theabove-mentioned ability to separately lock the orientation of the tulipassembly (106) relative to the pedicle screw (102) while. Consequently,the exemplary configurations of the tulip body (132), the inner member(134), and the expansion/contraction member (136) will each beindependently addressed in detail below with reference to FIGS. 7Athrough 9B.

FIG. 7A illustrates a perspective view of a tulip body (132) and FIG. 7Billustrates a cross-sectional view of the tulip body (132), according toone exemplary embodiment. As illustrated in FIGS. 7A and 7B, the tulipbody (132) includes a number of elements that facilitate reception of apedicle screw head portion (110; FIG. 3) and the ability to separatelylock the orientation of the tulip assembly (106; FIG. 1) relative to thepedicle screw (102; FIG. 1) and a positional location of a rod (104;FIG. 1) in the tulip assembly. According to one exemplary embodimentillustrated in FIGS. 7A and 7B, the tulip body (132) includes a bore(138), an upper portion (140), a lower portion (142), a rod receptionchannel (750), a declined plane (700), a rod locking surface (710), aninternal lip (143), an expansion/contraction member retention lip (720),a seating bore (730), and a taper bore (740).

According to one exemplary embodiment, the bore (138) is configured tofacilitate assembly of the tulip assembly (106; FIG. 4) before beingplaced onto the head portion of the pedicle screw (102; FIG. 1). In oneembodiment, the inner member (134; FIG. 5) and the split ring (136; FIG.5) portion of the tulip assembly may be inserted into the tulip body(132) upward through the bore (138) or through the lower portion (142)of the tulip body (132). Additionally, once the tulip assembly (106;FIG. 4) is pre-operatively assembled, the bore (138) facilitatesreception of the head portion (110; FIG. 3) of the pedicle screw (102;FIG. 3) during the initial coupling of the tulip assembly (106; FIG. 4)to the pedicle screw, as will be described in further detail below.

Continuing with FIGS. 7A and 7B, the declined plane (700), the rodreception channel, and the rod locking surface (710) of the upperportion (140) facilitate selective reception and retention of a rod(104; FIG. 1), according to one exemplary embodiment. As mentioned, therod (104; FIG. 1) may be inserted into the tulip body (132) eitherbefore or after placement of the tulip assembly (106; FIG. 4) on thehead portion (110; FIG. 3) of the pedicle screw (102; FIG. 3). Initialplacement of the rod (104; FIG. 1) is received by the tulip body (132)via the rod reception channel (750). Consequently, according to oneexemplary embodiment, the width of the rod reception channel (750) maybe substantially equal to or greater than the diameter of a desired rod(104; FIG. 1). However, according to other exemplary embodiments, therod reception channel (750) may be slightly narrower than the diameterof a desired rod (104; FIG. 1) to allow for a slight interference fitduring insertion. Once the rod (104; FIG. 1) is received by the tulipbody (132) via the rod reception channel (750), the tulip body (132) maybe oriented to positionally secure the received rod (104; FIG. 1) due toboth the angles of the declined plane (700) and the rod locking surface(710) as well as an interaction between the inner member (134; FIG. 5)and the rod, as will be further detailed below.

The tulip body (132) also includes a number of elements that allow therelative angular position (107; FIG. 1) of the tulip assembly (106; FIG.4) to be independently established relative to the pedicle screw (102;FIG. 1). Specifically, the internal lip (143), the expansion/contractionmember retention lip (720), the seating bore (730), and the taper bore(740) may, according to one exemplary embodiment, interact with othercomponents of the present pedicle screw system (100) to establish therelative angular position (107; FIG. 1) of the tulip assembly (106; FIG.4), as will be described below with reference to FIGS. 10 through 16B,

The inner member (134) of the present tulip assembly (106; FIG. 4) isillustrated in FIGS. 8A and 8B. As shown, the inner member (134)includes a main body (800) having an inner bore (850) formed therein.The inner bore (850) is substantially concentric with the bore (138;FIG. 7A) of the tulip body (132; FIG. 7A) when assembled. Additionally,the inner bore (850) is at least partially defined by the head receivingtaper (830) forming an inner surface of the main body (800). Further, asillustrated in FIGS. 8A and 8B, the main body (800) includes at leastone extension (810) protruding there from terminating in a positioninglip (815). The shape of the at least one extension (810) in conjunctionwith the main body (800) further defines a rod seat (820) configured toreceive and interface with the rod (104; FIG. 2). According to oneexemplary embodiment, the main body (800), the extension(s) (810), andthe positioning lip (815) are all sized to be received in the bore (138)of the tulip body (132) and then be rotatable within the tulip body(132), as will be described in more detail below. The rod seat (820),along with the inner wall of the extension(s) (810), operates incooperation with the tulip body (132) to receive, capture, andeventually positionally lock the rod (104) into the tulip assembly. Thebottom surface (158) of the main body (800) may engage theexpansion/contraction member (136; FIG. 5) and force theexpansion/contraction member down in the bore (138; FIG. 7A) of thetulip body (132; FIG. 7A), according to one exemplary embodiment.However, according to a preferred exemplary embodiment, the bottomsurface (158) of the main body (800) does not contact theexpansion/contraction member (136; FIG. 5) thereby allowing the innermember to achieve its full mechanical advantage on the head portion(110; FIG. 3) of the pedicle screw (102; FIG. 3). According to thisexemplary embodiment, the forced contraction of theexpansion/contraction member (136; FIG. 5) along with the radialconstraint provided by the seating bore (730; FIG. 7B) and the taperbore (740; FIG. 7B) of the tulip body (132; FIG. 7B), in combinationwith the mechanical advantage imparted by the inner member, generatessufficient radial pressure on the head portion (110; FIG. 3) of thepedicle screw (102; FIG. 3) to lock the relative angular position (107;FIG. 1) of the tulip body (132; FIG. 1) with respect to the pediclescrew (102; FIG. 1).

FIGS. 9A and 9B illustrate the elements of an expansion/contractionmember (136), commonly referred to as a split ring. As mentionedpreviously, the expansion/contraction member (136) is sized andconfigured to be received and retained in the lower portion (142; FIG.7A) of the tulip body (132; FIG. 7A). Accordingly, a number of featuresare formed on the expansion/contraction member (136) to facilitate boththe insertion of the expansion/contraction member (136) into the tulipbody (132; FIG. 7A) and to allow the expansion/contraction member (136)to receive the head portion (110; FIG. 3) of the pedicle screw (102;FIG. 3) while aiding in locking the relative angular position (107;FIG. 1) of the tulip body (132; FIG. 1).

Specifically, as illustrated in FIGS. 9A and 9B, the exemplaryexpansion/contraction member (136) includes a main member body (950)having an expansion gap (910) formed therein. According to one exemplaryembodiment, the expansion gap (910) is configured to facilitate theexpansion and contraction of the expansion/contraction member (136)without causing undue stresses on the member material. In addition tothe expansion gap (910), the expansion/contraction member (136) includesa lower head receiving orifice (920) that is configured to beconcentrically aligned with the inner bore (850; FIG. 8A) of the innermember (134; FIG. 8A) and the bore (138; FIG. 7A) of the tulip body(132; FIG. 7A) when assembled. According to one exemplary embodiment,the lower head receiving orifice (920) includes a lower head interfacingsurface (940) configured to initially receive the head portion (110;FIG. 3) of the pedicle screw (102; FIG. 3) and further be retained onthe head portion of the pedicle screw by the tulip body (132; FIG. 7A)during a reduction step, as will be described in further detail below.

Additionally, as illustrated in FIGS. 9A and 9B, theexpansion/contraction member (136) includes a translation stop (930) anda seating taper (900) formed in the member body (950). According to oneexemplary embodiment, the translation stop (930) is formed having anouter diameter associated with the expansion/contraction memberretention lip (720; FIG. 7B) formed in the tulip body (132; FIG. 7B).Consequently, as will be described below, the translation stop (930)interacts with the expansion/contraction member retention lip (720; FIG.7B) to provide a resistance to translation of the expansion/contractionmember during the insertion of the head portion (110; FIG. 3) of thepedicle screw (102; FIG. 3). Additionally, the expansion/contractionmember (136) includes a seating taper (900) that coincides with thetaper bore (740; FIG. 7B) of the tulip body (132; FIG. 7A). According toone exemplary embodiment, the seating taper (900) is configured to bepositioned within the taper bore (740; FIG. 7B) and create a mechanicaladvantage sufficient to lock the relative angular position (107; FIG. 1)of the tulip body (132; FIG. 1) with respect to the pedicle screw (102;FIG. 1). Particularly, the seating taper (900) of theexpansion/contraction member (136) frictionally contacts the taper bore(740; FIG. 7B) of the tulip body (132). Simultaneously, the lower headinterfacing surface (940) of the expansion/contraction member (136)frictionally engages the head portion (110; FIG. 3) of the pedicle screw(102; FIG. 3), as will be described in more detail below. In oneexemplary embodiment, the expansion/contraction member (136) isfabricated to be elastically expandable and contractible within therange of operations described herein. Further detail of the function andoperation of the present tulip assembly (106; FIG. 4) will be describedbelow with reference to FIGS. 10-16B.

Exemplary Implementation and Operation

FIG. 10 illustrates one method for installing the exemplary pediclescrew system (100; FIG. 1), according to one exemplary embodiment. Asillustrated in FIG. 10, the present exemplary method for installing thepedicle screw system (100; FIG. 1) includes inserting one or morepedicle screws in a patient's spinal system (step 1000). Once the one ormore pedicle screws are inserted in a patient's spinal system, the tulipassembly (106; FIG. 1) is installed over the head of the pedicle screw(step 1005). With the tulip assembly snapped over the head of thepedicle screw, the relative position of the tulip assembly may beoriented as desired relative to the pedicle screw (step 1010). When thedesired orientation established, the tulip may be retained on thepedicle screw during a reduction step (step 1020). Once the tulip isretained, according to one exemplary embodiment, the rod may be insertedin the tulip (step 1030), and the tulip assembly position relative tothe pedicle screw may be provisionally established by positioning theinner tulip member (step 1040). With the tulip position relative to thepedicle screw due to the positioning of the inner tulip member, thetulip body (132; FIG. 7B) may be partially rotated to retain the rod(step 1050) followed by a further rotation of the tulip body for a finallock of the rod (step 1060). Further details of each step of the presentexemplary method will be provided below with reference to FIGS. 11through 16B.

As illustrated in FIG. 10, the first step of the exemplary method is toinsert one or more pedicle screws in a patient's spinal system (step1000) corresponding to a desired number of pedicle screw systems (100;FIG. 1). The placement and/or number of pedicle screw systems (100;FIG. 1) to be used in a patient may be pre-operatively determined basedon a pre-operative examination of the patient's spinal system usingnon-invasive imaging techniques known in the art, such as x-ray imaging,magnetic resonance imaging (MRI), and/or fluoroscopy imaging, forexample.

With the one or more pedicle screws inserted into a patient's spinalsystem (step 1000), the tulip assembly may be snapped over the head of apreviously inserted pedicle screw (step 1005), as illustrated by thearrow in FIG. 11. According to one exemplary embodiment, the tulipassembly (106) may be intra-operatively (i.e., during surgery) coupledto the head portion (110) of the pedicle screw (102) and may bemaneuverable to achieve a desired placement, orientation, and/or angularposition (20; FIG. 1) of the tulip assembly (106) relative to thepedicle screw (102).

FIGS. 12A and 12B illustrate the tulip assembly (106) snapped onto thehead portion (110) of the pedicle screw (102). According to oneexemplary embodiment, when the tulip assembly (106) is snapped onto thehead portion (110) of the pedicle screw (102), the lower headinterfacing surface (940; FIG. 9B) of the expansion/contraction member(136) mates with the head portion (110) of the pedicle screw (102). Asthe tulip assembly (136) is pushed onto the head portion (110) of thepedicle screw (102), the expansion/contraction member (136) expands andsnaps onto the head portion (110). The expansion/contraction member(136) is initially pushed up into the bore (138; FIG. 7B) of the tulipbody (132), as described above. The bore (138; FIG. 7B) in the lowerportion (142; FIG. 7A) of the tulip body (132) permits theexpansion/contraction member (136) to float in the bore until it makescontact with the translation stop (930) as illustrated in FIG. 12B.Alternatively stated, as the expansion/contraction member (136) ispushed upwards inside of the tulip body (132) by the head portion (110)of the pedicle screw (102), the expansion/contraction member is stoppedfrom translating and sufficient clearance is present for theexpansion/contraction member to expand and snap around the head portion(110) of the screw (102). At this point of the installation method, thetulip assembly (106) may be rotationally coupled to the head portion(110) of the pedicle screw (102).

Once the tulip assembly (106) is at the desired position relative to thepedicle screw (102), the tulip assembly may then be rotated to achieve adesired orientation with respect to the pedicle screw (step 1010; FIG.10). It is understood that the relative angular position (107; FIG. 1)of a first tulip assembly (106) to a first pedicle screw (102) may bedifferent from the relative orientation of other pedicle screw systems(100; FIG. 1) located elsewhere on a patient's spine. In general, therelative, angular position (107; FIG. 1) of the tulip assembly (106;FIG. 1) to the pedicle screw (102) allows the surgeon to selectively andindependently orient and manipulate the tulip assemblies (106) of eachpedicle screw system (100; FIG. 1) installed into the patient to achieveand/or optimize the goals of the surgical procedure, which may involvecompressing, expanding, distracting, rotating, reinforcing, and/orotherwise correcting an alignment of at least a portion of a patient'sspine.

With the tulip assembly (106) positioned relative to the pedicle screw(step 1010; FIG. 10), a reduction step may be performed with the tulipassembly remaining on the pedicle screw (step 1020; FIG. 10). Asillustrated in FIGS. 13A and 13B, the reduction step is performed bypulling the tulip assembly (106) away from the head portion (110) of thepedicle screw (102), as illustrated by the arrow in FIG. 13B. As thetulip assembly (106) is translated along the head portion (110), theexpansion/contraction member (136) is contracted as it is seated in theseating bore (730) and the taper bore (740) of the tulip body (132).More specifically, according to one exemplary embodiment, the matingtapered surfaces, which comprise the head portion (110) of the pediclescrew (102), the lower head interfacing surface (940) and the seatingtaper (900) of the expansion/contraction member (136), and the seatingbore (730) and taper bore (740) of the bore (138; FIG. 7) of the tulipbody (132), cooperate to lock the tulip assembly (106) onto the headportion (110) of the pedicle screw.

The upward force applied to the tulip body (132), illustrated by thearrow of FIG. 13B, tends to cause compression and/or contraction of theexpansion/contraction member (136) because the expansion/contractionmember (136) is forced down further along the inner surface of the bore(138; FIG. 7) of the tulip body (132). Consequently, the seating taper(900) of the expansion/contraction member (136) interacts with the taperbore (740), resulting in added compression and/or contraction. Suchadditional compression and/or contraction of the expansion/contractionmember (136) substantially locks or fixes the tulip assembly (106) ontothe pedicle screw (102), thus preventing additional rotation,manipulation, loosening, and/or removal of the tulip assembly withrespect to the pedicle screw. In short, when the tulip assembly (106) isinitially placed onto the head portion (110) of the pedicle screw (102),the tulip assembly is free to move poly-axially in relation to thepedicle screw. Thus, the tulip assembly (106) remains free to rotate onthe pedicle screw (102) until it is locked onto the head portion (110)of the pedicle screw, where the locking will be described below.

In addition, as illustrated in FIGS. 13A and 13B, both the tulip body(132) and the inner member (134) are aligned to receive the rod (104;FIG. 11). For purposes of clarity, however, the rod (104; FIG. 11) isnot shown so that the features of the tulip assembly (106) that captureand lock the rod are more readily viewable. It will be understood thatthe tulip assembly (106) may be fixed to the pedicle screw (102) atvarious stages of the present exemplary installation of the pediclescrew system (100; FIG. 1). In one exemplary embodiment, the tulipassembly (106) is fixed onto the pedicle screw (102) before the rod(104; FIG. 11) is fixed or locked into the tulip assembly. In anotherembodiment, the tulip assembly (106) is fixed onto the pedicle screw(102) contemporaneously as the rod (104; FIG. 11) is fixed or lockedinto the tulip assembly. For ease of explanation, the present methodwill continue to be described according to the exemplary methodillustrated in FIG. 10.

Continuing with FIGS. 14A and 14B, once the reduction of theexpansion/contraction member (136) has been performed, the rod may beinserted in the tulip assembly (step 1030; FIG. 10) and the tulipposition relative to the pedicle screw may be provisionally locked bypositioning the inner tulip member (step 1040; FIG. 10). As illustrated,the rod (104) may be placed through the rod reception channel (750) andinto the rod seat portion (820) of the inner member (134). According toone exemplary embodiment, the rod reception channel (750) and the rodseat portion (820) of the inner member (134) are specifically sized toreceive the rod (104) without significant interference.

With the rod (104) inserted in the rod reception channel (step 1030),the tulip position relative to the pedicle screw may be provisionallylocked by positioning the inner tulip member (step 1040; FIG. 10). Asillustrated in FIG. 14B, the inner member (134) may be forced toward thehead portion (110) of the pedicle screw (102), either by a forcetranslated through the rod (104), or by another instrument. As the innermember (134) is pushed toward the head portion (110) of the pediclescrew (102), the positioning lip (815) is retained under the internallip (143) of the tulip body (132). As the inner member (134) is forceddownward such that the positioning lip (815) is retained under theinternal lip (143) of the tulip body, the head receiving taper (830)portion of the inner member engages the head portion (110) of thepedicle screw (102), imparting a friction inducing force thereon.According to one exemplary embodiment, the extensions (810) of the innermember (134) flex inward when pushed down and then expand to becomeengaged under the internal lip (143) of the tulip body (132). Thislongitudinal engagement to retain the inner member (134) compressedwithin the tulip body (132) may be accomplished either before or afterthe rod (104) is placed in the tulip assembly (106).

According to one exemplary embodiment, when the positioning lip (815) ofthe inner member (134) is placed under the internal lip (143) of thetulip body (132), the frictional force exerted on the head portion (110)of the pedicle screw (102) is maintained, provisionally locking thetulip position. According to one exemplary embodiment, the frictionprovided by the head receiving taper (830) portion of the inner memberis greater than the friction provided by the lower head interfacingsurface (940) and the seating taper (900) of the expansion/contractionmember (136). This variation of friction between the lower headinterfacing surface (940) and the head receiving taper (830) preventsscrew advancement when the outer housing is rotated for rod locking, asis described below. According to one exemplary embodiment, the variationof friction between the lower head interfacing surface (940) and thehead receiving taper (830) is achieved by varying their respectivetapers, and consequently, varying the mechanical advantage achieved byeach.

With the position of the tulip assembly (106) relative to the pediclescrew (102) established, the tulip body (132) may be partially rotatedto substantially retain the rod (step 1050; FIG. 10). More particularly,as illustrated in FIGS. 15A and 15B, the tulip body (132) may berotated, as indicated by the arrow R, causing the rod locking surface(710) of the tulip body (132) to engage the rod (104). According to oneexemplary embodiment, an angular rotation of approximately 30 degrees issufficient to substantially retain the rod (step 1050; FIG. 10) withinthe tulip assembly (106). The rod (104) may initially be retained on therod-capturing portion (760) (best shown in FIG. 7A) of the rod lockingsurface (710), according to one exemplary embodiment. In addition, afterthe tulip body (132) is partially rotated to capture the rod (104), therod locking surface (710), and particularly the rod-capturing portion(760) of the tulip body (132) prevent the tulip body (132) from splayingopen under operative and post-operative dynamic and static loading, forexample. Splaying is prevented due to the increased amount of tulip bodymaterial that is coupled up and over the rod (104), compared totraditional pedicle screw assemblies. When the tulip body (132) isrotated, the rod locking surface (710) engages the rod (104) and createssufficient interference with the rod to prevent the rod from slideablytranslating through the tulip assembly (106). The interference iscaused, according to one exemplary embodiment, between at least the rod(104), the rod locking surface (710) of the tulip body (132), and therod seat portion (820) of the inner member (134).

As the tulip body (132) is further rotated, as illustrated in FIGS. 16Aand 16B, the rod is placed in a final lock position within the tulipassembly (step 1060). According to one exemplary embodiment, as thetulip body (132) is further rotated, the rod locking surface (710)continues to force the rod (104) into the rod seat (820) of the innermember (134). As illustrated in the exemplary embodiment of FIG. 16B,when in the final lock position, the rod (104) is forced intosubstantially full engagement with the rod seat (820). Consequently, theresistive force exerted against the rod (104) increases the frictionalresistance provided by the rod locking surface (710) to prevent the rodfrom slideably translating within the tulip assembly (106).Additionally, the increased engagement between the rod seat (820) andthe rod (104) further forces the head receiving taper onto the headportion (110) of the pedicle screw (102), and increases the interactionbetween the taper bore (740) and the seating taper (900) such that theposition of the tulip assembly (106) relative to the pedicle screw (102)is further secured. According to one exemplary embodiment, the rotationof the tulip body (132) may be performed by inserting an instrument intothe rod reception channel (750) and forcing rotation thereof.Alternatively, the tulip body (132) may be independently rotated tosecure the rod (104) within the tulip assembly (106) by any number ofmethods including, but in no way limited to, a socket-type tool thatengages the upper outer surface of the tulip body (132).

During operation, the present exemplary pedicle screw system asdescribed, but not limited to the embodiments herein, is designed forfixation of bone material and/or bone segments during a surgicalprocedure, such as fusing spinal segments in which MIS techniques areemployed. For example, according to one exemplary embodiment, thepedicle screw system is inserted into the pedicles of a patient's spineand then interconnected with rods to provide support to the spine toallow for post-operative fusion of the spinal segments. While thepedicle screw can be inserted with the tulip assembly coupled with thepedicle screw, one embodiment for the installation of the pedicle screwsystem includes inserting the pedicle screw into the bone andsubsequently coupling the tulip assembly to the pedicle screw, wheresuch an approach has advantages over currently known pedicle screwsystem assemblies and/or installations.

In addition, according to a number of exemplary embodiments, variousstructural features of the pedicle screw system as described, but notlimited to the embodiments herein, may provide other advantages overexisting pedicle screw systems. First, the pedicle screw may be insertedinto the bone of a patient without the presence of the tulip assembly orrod, which permits the surgeon to place the screw and then performsubsequent inter-body work without having to work around the tulipassembly or the rod. Second, the tulip assembly includes a mechanism forcapturing the rod that eliminates problems associated with conventionalpedicle screws, such as cross-threading, because the exemplary pediclescrew systems disclosed herein do not use any threads to couple thetulip assembly to the pedicle screw or to capture and lock the rod intothe tulip assembly. Third, the interface between the head portion of thepedicle screw and the tulip assembly provide an initial lock, whichallows the angle of the tulip assembly to be set or fixed with respectto the pedicle screw before insertion of the rod and/or before the rodis captured in the tulip assembly. With this type of pedicle screwsystem, the surgeon has the ability to check and even double check theplacement, angle, and/or orientation regarding aspects of the pediclescrew system to facilitate, and even optimize, the compression,distraction, and/or other manipulation of the spinal segments. Further,the present exemplary pedicle screw system accommodates the new MIStechniques being applied to spinal operations.

One possible post-operative advantage of the present exemplary pediclescrew system is that the cooperation and interaction of the inner memberwith the tulip body of the tulip assembly substantially reduces, andmost likely prevents, the known problem of tulip splaying. Tulipsplaying is generally regarded as a post-operative problem caused by astressed rod forcing open portions of the tulip body, which eventuallyleads to the disassembly and likely failure of the pedicle screw systemwithin the patient. Yet another post-operative advantage of the pediclescrew systems is that unlike existing rod-coupling members orconstructs, the exemplary tulip assemblies described herein have asmaller size envelope (e.g., less bulky, lower profile, and/or morecompact shape) and are easier to place onto the pedicle screw, whencompared to traditional tulip assemblies. The smaller size and ease ofinstallation may reduce trauma to the soft-tissue regions in thevicinity of the surgical site, which in turn generally allows for aquicker recovery by the patient. Yet another possible advantage of thepresent exemplary pedicle screw system over traditional existing systemsis that all of the parts needed to lock the tulip assembly to thepedicle screw and to capture and lock the rod into the tulip assemblyare included within the tulip assembly. Accordingly, once the tulipassembly is snapped or otherwise coupled to the pedicle screw, noadditional locking cap or threaded fastener is needed to complete theassembly/installation of the pedicle screw system. According to aspectsdescribed herein, and as appended by the claims, the present exemplarypedicle screw systems permit insertion of the pedicle screw without thetulip assembly coupled thereto, locking the tulip assembly onto thepedicle screw, and subsequently capturing and locking the rod into thetulip assembly.

The preceding description has been presented only to illustrate anddescribe the present method and system. It is not intended to beexhaustive or to limit the present system and method to any precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching.

The foregoing embodiments were chosen and described in order toillustrate principles of the system and method as well as some practicalapplications. The preceding description enables others skilled in theart to utilize the method and system in various embodiments and withvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the present exemplary system and methodbe defined by the following claims.

1. A tulip assembly configured to be coupled to a head of a bonefixation device comprising: at least one inner member configured to fixsaid tulip assembly to said head of a bone fixation device; and an outermember including at least one engagement surface configured toselectively fix a rod in the tulip assembly via rotation of said outermember.
 2. The tulip assembly of claim 1, wherein said engagementsurface comprises a declining plane configured to force said rod intosaid at least one inner member when said outer member is rotated.
 3. Thetulip assembly of claim 1, wherein said at least one inner membercomprises: a first inner member disposed in a lower portion of saidouter member; a second inner member disposed in an upper portion of saidouter member; wherein said first inner member is elastically expandableto receive said head of a bone fixation device; and wherein said secondinner member is configured to interact with said rod when said outermember is rotated.
 4. The tulip assembly of claim 3, wherein said secondinner member comprises: a main body; at least one extension proximallyprotruding from said main body at terminating in a positioning lip; aninner bore formed in a distal end of said main body; and a frictioninducing taper formed on an inner wall of said body defined by saidinner bore; wherein said friction inducing taper is configured to engagesaid head of a bone fixation device to fix a position of said tulipassembly relative to said bone fixation device.
 5. The tulip assembly ofclaim 4, wherein said at least one proximally protruding extensiondefines a seat configured to receive said rod.
 6. The tulip assembly ofclaim 4, wherein: said outer member comprises an inner bore including aninternal lip circumferentially disposed in said upper portion of saidouter member; wherein said internal lip is configured to receive saidpositioning lip of said second inner member when engaged to positionallysecure said second inner member in said outer member.
 7. The tulipassembly of claim 4, wherein said first inner member comprises a ringconfigured to be elastically, diametrically expandable and contractible.8. The tulip assembly of claim 7, wherein said ring includes a splitthat permits a diameter of the ring to vary from a first, largerdiameter to a second, smaller diameter.
 9. The tulip assembly of claim4, wherein said first inner member further comprises: a frictioninducing tapered inner surface configured to seat against said headportion of said pedicle screw; and an external seating taper surfaceconfigured to induce contraction of said first inner member wheninteracting with a taper bore of said tulip body.
 10. The tulip assemblyof claim 9, wherein said friction inducing tapered inner surface andsaid friction inducing taper of said second inner member have differenttaper angles.
 11. The tulip assembly of claim 10, wherein said frictioninducing taper of said second inner member imparts a greater frictionalforce on said head of a bone fixation device than said friction inducingtapered inner surface of said first inner member.
 12. A tulip assemblyconfigured to be coupled to a head of a bone fixation device comprising:an outer housing member including an upper portion and a lower portionhaving an internal tapered edge in said lower portion; a first innermember disposed in a lower portion of said outer member, said firstinner member being elastically expandable to receive said head of a bonefixation device; a second inner member disposed in an upper portion ofsaid outer member, said second inner member being configured to receivea distraction rod; wherein said first inner member includes an externaltapered edge and an internal tapered edge, said external tapered edgebeing configured to mate with said internal tapered edge of said outerhousing member to compress said first inner member.
 13. The tulipassembly of claim 12, wherein: said internal tapered edge of said firstinner member is configured to engage a lower portion of said head of abone fixation device; said second inner member comprises an internaltapered edge to engage an upper portion of said head of a bone fixationdevice; and wherein said internal tapered edge of said first innermember and said internal tapered edge of said second inner member createa mechanical advantage to maintain an angle of said tulip assemblyrelative to said bone fixation device.
 14. The tulip assembly of claim13, wherein said mechanical advantage created by said internal taperededge of said first inner member is less than said mechanical advantagecreated by said internal tapered edge of said second inner member. 15.The tulip assembly of claim 13, wherein said second inner member furthercomprises an engagement portion in contact with said first inner memberto maintain a contraction of said first inner member.
 16. The tulipassembly of claim 15, wherein: said outer member comprises an inner boreincluding an internal lip circumferentially disposed in said upperportion of said outer member; and wherein said second inner memberfurther comprises at least one positioning lip configured to engage saidinternal lip of said outer member to maintain an engaged position ofsaid second inner member.
 17. The tulip assembly of claim 13, whereinsaid first inner member is further configured to fix said tulip assemblyto said head of a bone fixation device after expanding to receive saidhead.
 18. The tulip assembly of claim 13, wherein said outer housingfurther comprises: at least one engagement surface configured toselectively fix a rod in the tulip assembly via rotation of said outermember; said engagement surface including a decline plane that forcessaid rod into said second inner member when said outer member isrotated.
 19. The tulip assembly of claim 18, wherein said engagementsurface is further configured to force said second inner member intosaid head of a bone fixation device, further seating said first innermember when said outer member is rotated while a rod is present in saidtulip assembly.
 20. A tulip assembly configured to be coupled to a headof a bone fixation device comprising: at least one inner memberconfigured to fix an angular position of said tulip assembly relative tosaid bone fixation device; and an outer member including at least oneengagement surface configured to selectively fix a rod in the tulipassembly via rotation of said outer member; wherein said fixation of anangular position of said tulip assembly relative to said bone fixationdevice and said rod fixation are separate operations.
 21. A tulipassembly configured to be coupled to a head of a bone fixation devicecomprising: an outer housing member including an upper portion and alower portion having an inner bore with an internal lipcircumferentially disposed in said upper portion of said outer memberand an internal tapered edge formed in said lower portion; a first innermember disposed in a lower portion of said outer member, said firstinner member being elastically expandable to receive said head of a bonefixation device, wherein said first inner member includes an externaltapered edge and an internal tapered edge, said external tapered edgebeing configured to mate with said internal tapered edge of said outerhousing member to compress said first inner member, said internaltapered edge of said first inner member being configured to engage alower portion of said head of a bone fixation device; a second innermember configured to receive a distraction rod disposed in an upperportion of said outer member, said second inner member including aninternal tapered edge to engage an upper portion of said head of a bonefixation device, wherein said second inner member further includes atleast one positioning lip configured to engage said internal lip of saidouter member to maintain an engaged position of said second innermember; wherein said internal tapered edge of said first inner memberand said internal tapered edge of said second inner member create amechanical advantage to maintain an angle of said tulip assemblyrelative to said bone fixation device; and wherein said outer memberincludes at least one engagement surface configured to selectively fix arod in the tulip assembly via rotation of said outer member, saidengagement surface including a decline plane that forces said rod intosaid second inner member when said outer member is rotated.
 22. Thetulip assembly of claim 21, wherein said engagement surface is furtherconfigured to force said second inner member into said head of a bonefixation device, further seating said first inner member when said outermember is rotated while a rod is present in said tulip assembly.
 23. Thetulip assembly of claim 21, wherein said mechanical advantage created bysaid internal tapered edge of said first inner member is less than saidmechanical advantage created by said internal tapered edge of saidsecond inner member.
 24. A pedicle screw system comprising: a pediclescrew having a threaded portion and a head portion; and a tulip assemblyincluding at least one inner member configured to fix said tulipassembly to said head portion, and an outer member including at leastone engagement surface configured to selectively fix a rod in the tulipassembly via rotation of said outer member.
 25. The pedicle screw systemof claim 24, wherein said engagement surface comprises a declining planeconfigured to force said rod into said at least one inner member whensaid outer member is rotated.
 26. The pedicle screw system of claim 24,wherein said at least one inner member of said tulip assembly comprises:a first inner member disposed in a lower portion of said outer member; asecond inner member disposed in an upper portion of said outer member;wherein said first inner member is elastically expandable to receivesaid head portion of said pedicle screw; and wherein said second innermember is configured to interact with said rod when said outer member isrotated.
 27. The pedicle screw system of claim 26, wherein said secondinner member comprises: a main body; at least one extension proximallyprotruding from said main body at terminating in a positioning lip; aninner bore formed in a distal end of said main body; and a frictioninducing taper formed on an inner wall of said body defined by saidinner bore; wherein said friction inducing taper is configured to engagesaid head portion of said pedicle screw to fix a position of said tulipassembly relative to said pedicle screw.
 28. The pedicle screw system ofclaim 27, wherein: said outer member comprises an inner bore includingan internal lip circumferentially disposed in said upper portion of saidouter member; wherein said internal lip is configured to receive saidpositioning lip of said second inner member when engaged to positionallysecure said second inner member in said outer member.
 29. The pediclescrew system of claim 24, wherein said first internal member comprises asplit ring.
 30. The pedicle screw system of claim 29, wherein said firstinner member further comprises: a friction inducing tapered innersurface configured to seat against said head portion of said pediclescrew; and an external seating taper surface configured to inducecontraction of said first inner member when interacting with a taperbore of said tulip body.
 31. The pedicle screw system of claim 30,wherein said friction inducing tapered inner surface and said frictioninducing taper of said second inner member have different taper angles.32. The pedicle screw system of claim 31, wherein said friction inducingtaper of said second inner member imparts a greater frictional force onsaid head portion of said pedicle screw than said friction inducingtapered inner surface of said first inner member.
 33. A pedicle screwsystem comprising: a pedicle screw having a threaded portion and a headportion; and a tulip assembly including an outer housing memberincluding an upper portion and a lower portion having an internaltapered edge in said lower portion, a first inner member disposed in alower portion of said outer member, said first inner member beingelastically expandable to receive said head portion of said pediclescrew, a second inner member disposed in an upper portion of said outermember, said second inner member being configured to receive adistraction rod, wherein said first inner member includes an externaltapered edge and an internal tapered edge, said external tapered edgebeing configured to mate with said internal tapered edge of said outerhousing member to compress said first inner member.
 34. The pediclescrew system of claim 33, wherein: said internal tapered edge of saidfirst inner member is configured to engage a lower portion of said headportion; said second inner member comprises an internal tapered edge toengage an upper portion of said head portion; and wherein said internaltapered edge of said first inner member and said internal tapered edgeof said second inner member create a mechanical advantage to maintain anangle of said tulip assembly relative to said pedicle screw.
 35. Thepedicle screw system of claim 34, wherein said mechanical advantagecreated by said internal tapered edge of said first inner member is lessthan said mechanical advantage created by said internal tapered edge ofsaid second inner member.
 36. A method of fixing a tulip assembly to apedicle screw comprising: inserting said pedicle screw into a bone, saidpedicle screw including a head portion; expanding a first inner memberover and head portion of said pedicle screw after said pedicle screw isinserted into a bone; fixing an angle of said tulip assembly relative tosaid pedicle screw using said first inner member and a second innermember; and positionally locking a rod in said tulip member after saidangle is fixed.
 37. The method of claim 36, wherein said step of fixingan angle of said tulip assembly relative to said pedicle screwcomprises: compressing said first inner member to frictionally engage alower section of said head portion with an inner tapered surface of saidfirst inner member; and frictionally engaging an upper section of saidhead portion with a taper disposed on a lower portion of said secondinner member.
 38. The method of claim 37, wherein said taper disposed ona lower portion of said second inner member engages said head portionwith a greater frictional force than said inner tapered surface of saidfirst inner member.
 39. A method of fixing a tulip assembly to a pediclescrew comprising: inserting said pedicle screw into a bone, said pediclescrew including a head portion; expanding a first inner member over andhead portion of said pedicle screw after said pedicle screw is insertedinto a bone; fixing an angle of said tulip assembly relative to saidpedicle screw using said first inner member and a second inner member;inserting a rod into said tulip assembly; and positionally locking saidrod in said tulip assembly after said angle is fixed by rotating anouter member of said tulip assembly including at least one rodengagement surface.
 40. The method of claim 39, wherein said step offixing an angle of said tulip assembly relative to said pedicle screwcomprises: compressing said first inner member to frictionally engage alower section of said head portion with an inner tapered surface of saidfirst inner member; and frictionally engaging an upper section of saidhead portion with a taper disposed on a lower portion of said secondinner member.
 41. The method of claim 40, wherein said taper disposed ona lower portion of said second inner member engages said head portionwith a greater frictional force than said inner tapered surface of saidfirst inner member.
 42. The method of claim 40, further comprisingcompressing said first inner member with said second inner member tofurther engage said first inner member with said head portion.